CENTRAL DOGMA OF GENE EXPRESSION TRANSCRIPITION AND TRANSLATION

 Transcription  It is the process of synthesis of RNA from a DNA template by RNA polymerase enzymes and a number of associated proteins

Replication Transcription Definition DNA synthesis from DNA template. RNA synthesis from DNA template. Character Complete (The entire chromosome is normally copied). Selective (Only particular genes are transcribed at any one time, and some portions of the DNA genome are never transcribed). Template The two DNA strands serve as template. Only one of the two strands serves as template.

Replication Transcription Polymerization DNA polymerase (DNA polymerase cannot initiate strand synthesis). . RNA polymerase. (RNA polymerase can). RNA primer Required Not required Required substrates d ATP, d GTP, d CTP and d TTP ATP, GTP, CTP, UTP

Replication Transcription (high –fidelity DNA synthesis). 5` 3` -Direction of synthesis 5` 3` 5` 3` -proofreading activity (3`-- 5` exonuclease ). Present (high –fidelity DNA synthesis). Absent (low-fidelity RNA synthesis).

The genetic information of the cell is stored and transmitted in the nucleotide sequences of DNA. Genetic code expressed DNA language (ATCG) is called the CODE same genetic code, expressed mRNA language, (UAGC) is called the CODON CODONS are always written from 5' to 3'

Expression of this genetic information involves two stages:- The first stage is transcription to form mRNA that carries specific and precise messages in the form of codons from DNA to the cytoplasmic sites of protein synthesis. ( Ribosomes) The second stage is translation of the nucleotide sequence of a mRNA (Codons) into an amino acid sequence of a protein.

Components of translation process  mRNA as a carrier of genetic information. tRNA as an adapter molecule, which recognizes an amino acid on one end and its corresponding codon on the other end. Ribosomes as the molecular machine coordinating the interaction between mRNA, tRNA, the enzymes and the protein factors required for protein synthesis.

Genetic Code It is the sequence of nucleotides along the DNA that can be translated into the amino acids of proteins. It is the relation between sequence of nucleotides in DNA (or in m RNA) and the sequence of amino acids in a polypeptide chain.

The genetic code is made up of a collection of codons. Codons are the individual words in the genetic code dictionary. Each codon is composed of 3 nucleotide bases.

Codon can be defined as: the sequence of three nucleotide bases on mRNA which determines the type and the position of the amino acid that will enter in the structure of protein molecule.

If the code were a triplet, then the four bases(G,C,U,A) could supply 64 different triplets (43 = 64), far more than needed to code for 20 different amino acids. The code is a triplet code. TERMINATORCODONS UAA,UAG& UGA START CODON:- AUG

 61 triplets encode for amino acids; the remaining 3 are stop codons, which signal termination of protein synthesis. (UAA,UAG,UGA) The one codon that stands for methionine is also a start codon signaling protein synthesis initiation.

Characters of genetic code 1-Genetic code is degenerate i.e. multiple codons can code for the same amino acid except tryptophan and methionine. examples: a. AUU, AUC & AUA code ile b.GUU,GUC,GUA&GUG code val c. UAU & UAC code tyr

Wobble theory: The 3rd nucleotide in a codon is less important than the other two in determining the specific amino acid to be incorporated I (inosine) can be found in the anti-codon.

2- Genetic code is unambiguous i. e 2- Genetic code is unambiguous i.e. each codon specifies no more than one amino acid 3- Genetic code is non-overlapping and Commaless i.e. each base used only once

Mutations are permanent changes in a DNA sequence. Gene Mutation Mutations are permanent changes in a DNA sequence. This altered DNA sequence can be reflected by changes in the base sequence of mRNA, and, sometimes, by changes in the amino acid sequence of a protein. Mutations can cause genetic diseases

Proteomics Proteomics is the study of the structure, function and interaction of cellular proteins Proteome Cellular Proteins

Gene Expression